Losses of soil carbon by converting tropical forest to plantations: erosion and decomposition estimated by δ13C

Indonesia lost more tropical forest than all of Brazil in 2012, mainly driven by the rubber, oil palm, and timber industries. Nonetheless, the effects of converting forest to oil palm and rubber plantations on soil organic carbon (SOC) stocks remain unclear. We analyzed SOC losses after lowland rainforest conversion to oil palm, intensive rubber, and extensive rubber plantations in Jambi Province on Sumatra Island. The focus was on two processes: (1) erosion and (2) decomposition of soil organic matter. Carbon contents in the Ah horizon under oil palm and rubber plantations were strongly reduced up to 70% and 62%, respectively. The decrease was lower under extensive rubber plantations (41%). On average, converting forest to plantations led to a loss of 10 Mg C ha^?1 after about 15 years of conversion. The C content in the subsoil was similar under the forest and the plantations. We therefore assumed that a shift to higher δ¹³C values in plantation subsoil corresponds to the losses from the upper soil layer by erosion. Erosion was estimated by comparing the δ¹³C profiles in the soils under forest and under plantations. The estimated erosion was the strongest in oil palm (35 ± 8 cm) and rubber (33 ± 10 cm) plantations. The ¹³C enrichment of SOC used as a proxy of its turnover indicates a decrease of SOC decomposition rate in the Ah horizon under oil palm plantations after forest conversion. Nonetheless, based on the lack of C input from litter, we expect further losses of SOC in oil palm plantations, which are a less sustainable land use compared to rubber plantations. We conclude that δ¹³C depth profiles may be a powerful tool to disentangle soil erosion and SOC mineralization after the conversion of natural ecosystems conversion to intensive plantations when soils show gradual increase of δ¹³C values with depth.     

Variability of soil carbon sequestration capability and microbial activity of different types of salt marsh soils at Chongming Dongtan

Variations in the soil carbon sequestration capability of different types of salt marsh soils at Chongming Dongtan and its influencing factors were studied by analyzing the soil organic carbon (SOC) content, organic matter input and microbial activities. The results indicated that the total SOC content at Area A (southeast of Dongtan, sandy soil with Phragmites communis) was only 46.11% of that of Area B (northeast of Dongtan, clay soil with mixed P. communis and Spartina alterniflora) (P = 0.000 < 0.05), but their organic matter input per year was almost identical. These findings implied that Area B had a lower output of SOC. The microbial biomass at Area A was 3.83 times greater than that at Area B (P = 0.049 < 0.05); the soil catalase and invertase activities at Area A, which were related to carbon metabolism, were 60.31% (P = 0.006 < 0.05) and 34.33% (P = 0.021 < 0.05) higher than at Area B, respectively; and the soil respiration at Area A was also higher than at Area B. These findings implied that the microbial activities at Area A were greater than those at Area B, and therefore the carbon metabolism was rapid, resulting in increased SOC output at Area A. Increased water content and salinity in the clay soil at Area B may inhibit the microbial activities, thereby reducing the decomposition of the organic matter and enhancing carbon sequestration. In addition, some artificial measures for controlling spread of S. alterniflora at Area B (mowing/digging and tillage (M + D); mowing/digging and tillage/waterlogging (M + D + W)) were found to generally improve the microbial activity of soil, thereby increasing SOC output. However, when the two different physical controlling modes were compared, the SOC and microbial activities of the soil subjected to the M + D + W treatment were relatively high and low, respectively, due to waterlogging restraining the microbial metabolism. These findings indicated that the difference in microbial activities was the important factor leading to variability in the SOC sequestration capability between Areas A and B. Additionally, with the exception of soil texture and vegetation types, environmental conditions and artificial turbulence also influenced microbial activities of soil, and hence SOC output and organic carbon sequestration capability.     

Effect of long-term nutrient managements on biological and biochemical properties of semi-arid tropical Alfisol during maize crop development stages

Understanding the influence of organic or inorganic nutrient management on soil biology and biochemistry during crop growth may help to develop more sustainable fertilization strategies. Hence, the biological variables including soil organic carbon (SOC), microbial biomass carbon (MBC), six cultivable microbial communities, five hydrolytic enzymes activity and soil respiratory indices from a long-term fertility experiment field (>100 years) were assessed at different growth stages of maize. The samples were taken from four long-term treatments viz., control (no fertilization), balanced inorganic fertilizers (IC), organic amendments (OM) and integrated nutrient management (INM, organic manure plus chemical fertilizers) at five different stages of maize cropping (S1, pre-cropping; S2, five days after sowing; S3, vegetative; S4, flowering; S5, after harvesting). Responses of most of the assessed parameters to organic fertilization (OM and INM) were significantly higher than those from inorganically managed and control soils. There was significant difference in SOC due to long-term nutrient managements (OM > INM > IC > control) but not due to growth stages of maize. MBC was also higher in OM and INM compared to IC and control and found significantly different at growth stages of maize. Values of microbial counts and assessed enzyme activities were highest at vegetative stage of maize following a declined trend at later stages. The respiration studies indicate a difference between the responses of substrate induced respiration rate (SIR) and metabolic quotient (qCO₂). SIR was more significantly influenced by long-term nutrient managements than crop stages, while qCO₂ was by early stage of maize growth (S2) alone. The principal component analysis (PCA) identifies MBC, qCO₂, SIR, dehydrogenase, phosphatase and aryl sulphatase and counts of Actinobacteria and diazotrophs as major drivers for the variability among the samples. PCA discriminated OM and INM samples from IC and control and vegetative stage of maize from other stages. The interaction effects of long-term nutrient managements and maize growth stages were found significant to MBC, counts of Actinobacteria and diazotrophs and activities of dehydrogenase, acid phosphatase and aryl sulphatase. However, the resilience of semi-arid tropical soil, independent of long-term nutrient management adoptions, was not affected due to maize growth. The present study thus provides some reliable biological indicators to monitor the semi-arid tropical soils, those influenced by nutrient managements.     

Short‐term soil carbon sink potential of oil palm plantations

Oil palm plantations cover ≈14.6 million ha worldwide and the total area under cultivation is expected to increase during the 21st century . Indonesia and Malaysia together account for 87% of global palm oil production and the combined harvested area in these countries has expanded by 6.5 million ha since 1990. Despite this, soil C cycling in oil palm systems is not well quantified but such information is needed for C budget inventories. We quantified soil C storage (root biomass, soil organic matter (SOM) and microbial biomass) and losses [potential soil respiration (R_s) and soil surface CO₂ flux (F_s)] in mineral soils from an oil palm plantation chronosequence (11–34 years since planting) in Selangor, Malaysia. There were no significant effects of plantation age on SOM, microbial biomass, R_s or F_s, implying soil C was in dynamic equilibrium over the chronosequence. However, there was a significant increase in root biomass with plantation age, indicating a short‐term C sink. Across the chronosequence, R_s was driven by soil moisture, soil particle size, root biomass and soil microbial biomass N but not microbial biomass C. This suggests that the nutrient status of the microbial community may be of equal or greater importance for soil CO₂ losses than substrate availability and also raises particular concerns regarding the addition of nitrogenous fertilizer, i.e. increased yields will be associated with increased soil CO₂ emissions. To fully assess the impact of oil palm plantations on soil C storage, initial soil C losses following land conversion (e.g. from native forest or other previous plantations) must be accounted for. If initial soil C losses are large, our data show that there is no accumulation of stable C in the soil as the plantation matures and hence the conversion to oil palm would probably represent a net loss of soil C.     

Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Afrotropical ant-following birds are vulnerable to forest loss and disturbance, but critical habitat thresholds regarding their abundance and species richness in human-dominated landscapes, including industrial oil palm plantations, have never been assessed. We measured forest cover through Landsat imagery and recorded species richness and relative abundance of 20 ant-following birds in 48 plots of 1-km², covering three landscapes of Southwest Cameroon: Korup National Park, smallholder agroforestry areas (with farms embedded in forest), and an industrial oil palm plantation. We evaluated differences in encounter frequency and species richness among landscapes, and the presence of critical thresholds through enhanced adaptive regression through hinges. All species were detected in Korup National Park and the agroforestry landscape, which had similar forest cover (>85%). Only nine species were found in the oil palm plantation (forest cover = 10.3 ± 3.3%). At the 1-km² scale, the number of species and bird encounters were comparable in agroforests and the protected area: mean species richness ranged from 12.2 ± 0.6 in the park and 12.2 ± 0.6 in the agroforestry matrix to 1.0 ± 0.4 in the industrial oil palm plantation; whereas encounters decreased from 34.4 ± 3.2 to 26.1 ± 2.9 and 1.3 ± 0.4, respectively. Bird encounters decreased linearly with decreasing forest cover, down to an extinction threshold identified at 24% forest cover. Species richness declined linearly by ca. one species per 7.4% forest cover lost. We identified an extinction threshold at 52% forest cover for the most sensitive species (Criniger chloronotus, Dicrurus atripennis, and Neocossyphus poensis). Our results show that substantial proportions of forests are required to sustain complete ant-following bird assemblages in Afrotropical landscapes and confirm the high sensitivity of this bird guild to deforestation after industrial oil palm development. Securing both forest biodiversity and food production in an Afrotropical production landscape may be best attained through a combination of protected areas and wildlife-friendly agroforestry.     

Effect of the replacement of tropical forests with tree plantations on soil organic carbon levels in the Jomoro district,Ghana

Background and aims

In the Jomoro district in Ghana, tree plantations were the first cause of deforestation in the past, drastically reducing the area occupied by primary forests. The aim of this study was to quantify soil organic carbon (SOC) losses due to a change in land use from primary forest to tree plantations (cocoa, coconut, rubber, oil palm) on the different substrates of the district. Secondary forests and mixed plantations were also included in the study.

Methods

Soils were sampled at different depths up to 100 cm along a series of chronosequences in each of the three substrates (Granite, Lower Birrimian and Tertiary Sands) present in the area.

Results

The highest SOC losses in the 0–30 cm layer were caused by the conversion of primary forests to tree plantations: cocoa ?61 % of the original SOC stock, coconut ?55 %, rubber ?35 % and oil palm 28 %, while mixed plantations and secondary forests showed a loss of 23 % and 21 % of the original SOC stock, respectively. C losses were less apparent from the entire profile (to a depth of 100 cm).

Conclusions

All conversions to tree plantations caused substantial SOC losses, comparable to the conversion of forests to agricultural systems. Secondary forests and mixed plantations were the only sustainable land uses that restricted SOC losses considerably.     

Environmental indicators for estimating the potential soil respiration rate in alpine zone

Soil respiration is the main form of carbon flux from soil to atmosphere in the global carbon cycle. The effect of temperature on soil respiration rate is important in evaluating the potential feedback of soil organic carbon to global warming. We incubated soils from the alpine meadow zone and upper rocky zone along an altitudinal gradient (4400–5500 m a.s.l.) on the Tibetan Plateau under various temperature and soil moisture conditions. We evaluated the potential effects of temperature and soil moisture on soil respiration and its variation across altitudes. Soil respiration rates increased as the temperature increased. At 60% of soil water content, they averaged 0.21–5.33 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.11–0.50 μmol g soil⁻¹ day⁻¹ in the rocky zone over the experimental temperature range. Soil respiration rates in the rocky zone did not increase between 25 and 35 °C, probably because of heat stress. Rates of decomposition of organic matter were high in the rocky zone, where the CN ratio was smaller than in the middle altitudes. Soil respiration rates also increased with increasing soil water content from 10% to 80% at 15 °C, averaging 0.04–2.00 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.03–0.35 μmol g soil⁻¹ day⁻¹ in the rocky zone. Maximum respiration rates were obtained in the middle part of the alpine slope in any case of experimental temperature and soil moisture. The change patterns in soil respiration rate along altitude showed similar change pattern in soil carbon content. Although the altitude is a variable including various environmental factors, it might be used as a surrogate parameter of soil carbon content in alpine zone. Results suggest that temperature, soil moisture and altitude are used as appropriate environmental indicators for estimating the spatial distribution of potential soil respiration in alpine zone.     

Comparison of boosted regression tree and random forest models for mapping topsoil organic carbon concentration in an alpine ecosystem

Soil organic carbon (SOC) plays an important role in soil fertility and carbon sequestration, and a better understanding of the spatial patterns of SOC is essential for soil resource management. In this study, we used boosted regression tree (BRT) and random forest (RF) models to map the distribution of topsoil organic carbon content at the northeastern edge of the Tibetan Plateau in China. A set of 105 soil samples and 12 environmental variables (including topography, climate and vegetation) were analyzed. The performance of the models was evaluated using a 10-fold cross-validation procedure. Maps of the mean values and standard deviations of SOC were generated to illustrate model variability and uncertainty. The results indicate that the BRT and RF models exhibited very similar performance and yielded similar predicted distributions of SOC. The two models explained approximately 70% of the total SOC variability. The BRT and RF models robustly predicted the SOC at low observed SOC values, whereas they underestimated high observed SOC values. This underestimation may have been caused by biased distributions of soil samples in the SOC space. Vegetation-related variables were assigned the highest importance in both models, followed by climate and topography. Both models produced spatial distribution maps of SOC that were closely related to vegetation cover. The SOC content predicted by the BRT model was clearly higher than that of the RF model in areas with greater vegetation cover because the contributions of vegetation-related variables in the two models (65% and 43%, respectively) differed significantly. The predicted SOC content increased from the northwestern to the southeastern part of the study area, average values produced by the BRT and RF models were 27.3 g kg⁻¹ and 26.6 g kg⁻¹, respectively. We conclude that the BRT and RF methods should be calibrated and compared to obtain the best prediction of SOC spatial distribution in similar regions. In addition, vegetation variables, including those obtained from remote sensing imagery, should be taken as the main environmental indicators and explicitly included when generating SOC maps in Alpine environments.     

Microbiological indicators of soil quality and degradation following conversion of native forests to continuous croplands

Deforestation resulting from forest conversion to agricultural land use is an important issue worldwide. This phenomenon is known to influence the activity and size of soil microbial community due to changes in environmental conditions with subsequent losses of soil organic matter (SOM) and soil quality degradation. The objective of this study was to investigate the relationship between soil organic carbon (SOC) losses and enzyme activities following land use conversion from native forests to continuous croplands. The amount of soil microbial biomass carbon (SMBC) and the activity of five soil enzymes (i.e., urease, invertase, alkaline phosphatase, acid phosphatase and arylsulfatase) were measured in croplands derived from forests and adjacent natural forests all on similar soil type at Gorgan site located in Northeast Iran. The content of SMBC decreased (47–83%) with deforestation at both soil sampling depths (0–20 and 20–40 cm). With the exception of phosphatases, the absolute activities of soil enzymes (activity on a soil mass basis) tended to decrease significantly (15–35%) with continuous cultivation. However, the specific enzyme activities expressed either per unit of SOC or SMBC tended to increase (about 1.5–5.5 times) with conversion of forestlands to croplands. The significant positive correlation between enzyme activity per SMBC and C turnover rate may imply that a faster C cycle and loss due to deforestation is related to a greater enzymatic activity by a smaller size of microbial biomass in cropland soils. In brief, the specific activities of soil enzymes could be used to reveal SOM losses and soil degradation in natural forest ecosystems, and to identify changes in soil quality and fertility following deforestation. Changes or improvements in soil management such as cessation of cultivation or implementing agricultural practices that stop or minimize soil disturbance are most likely needed to stop further soil degradation, restore soil quality and rebuild SOC stocks to offset CO₂ emissions in these ecosystems.     

Soil carbon balance following conversion of grassland to oil palm

Oil palm (Elaeis guineensis Jacq.) crops are expanding rapidly in the tropics, with implications for the global carbon cycle. Little is currently known about soil organic carbon (SOC) dynamics following conversion to oil palm and virtually nothing for conversion of grassland. We measured changes in SOC stocks following conversion of tropical grassland to oil palm plantations in Papua New Guinea using a chronosequence of plantations planted over a 25‐year period. We further used carbon isotopes to quantify the loss of grassland‐derived and gain in oil palm‐derived SOC over this period. The grassland and oil palm soils had average SOC stocks of 10.7 and 12.0 kg m^?2, respectively, across all the study sites, to a depth of 1.5 m. In the 0–0.05 m depth interval, 0.79 kg m^?2 of SOC was gained from oil palm inputs over 25 years and approximately the same amount of the original grass‐derived SOC was lost. For the whole soil profile (0–1.5 m), 3.4 kg m^?2 of SOC was gained from oil palm inputs with no significant losses of grass‐derived SOC. The grass‐derived SOC stocks were more resistant to decrease than SOC reported in other studies. Black carbon produced in grassfires could partially but not fully account for the persistence of the original SOC stocks. Oil palm‐derived SOC accumulated more slowly where soil nitrogen contents where high. Forest soils in the same region had smaller carbon stocks than the grasslands. In the majority of cases, conversion of grassland to oil palm plantations in this region resulted in net sequestration of soil organic carbon.     

Towards the application of soil organic matter as an indicator of forest ecosystem productivity: Deriving thresholds,developing monitoring systems,and evaluating practices

Soil organic matter (SOM), typically measured as soil organic carbon (SOC), has been widely recognized as a critical linkage between forest management and long-term site productivity. However, its use as an indicator of sustainable forest management practices has been limited both by difficulties in detecting changes in soil carbon due to inherent high variability and by challenges associated with determining appropriate thresholds for loss. In this study we evaluate a methodology for using field measures of total SOC (forest floor to 60 cm depth in mineral soil) in conjunction with a mechanistic forest growth model to derive threshold values for total SOC with respect to the maintenance of ecosystem productivity for a lodgepole pine (Pinus contorta) forest in the central interior region of British Columbia. We also examine the practicality of implementing a sustainable forest management (SFM) monitoring program around this measure and the potential long-term impact of alternative management scenarios on the indicator.Total SOC contents for the different site types sampled in the Quesnel region ranged from 35 to 57 t ha^?1. Long-term simulations of biomass extraction over several rotations showed a near 1:1 ratio in the relative decline of ecosystem productivity associated with relative declines in total SOC. A power analysis revealed that a mean sampling intensity of n = 12–25 and n = 8–17 would be required to detect 20% and 30% losses of total SOC, respectively, depending on the level of statistical power desired. The sampling intensity required for an effective monitoring program was significantly reduced by summing SOC for all soil layers to limit sampling error related to determination of layer boundaries. A modelling analysis of the effect of rotation length on SOC for the Quesnel forest types, suggests that rotation lengths shorter than 75 years should be avoided to prevent declines in ecosystem productivity. Our results confirm that the combination of modelling and statistical techniques can be successfully used to develop cost-efficient monitoring plans of sustainability of forest management, with SOC as a valid indicator of ecosystem productivity.     

Long-term tillage effects on soil organic carbon and dissolved organic carbon in a purple paddy soil of Southwest China

The impact of conservation tillage practices on soil carbon has been of great interest in recent years. Conservation tillage might have the potential to enhance soil carbon accumulation and alter the depth distribution of soil carbon compared to conventional tillage based systems. Changes in the soil organic carbon (SOC) as influenced by tillage, are more noticeable under long-term rather than short-term tillage practices. The objective of this study was to determine the impacts of long-term tillage on SOC and dissolved organic carbon (DOC) status after 19 years of four tillage treatments in a Hydragric Anthrosol. In this experiment four tillage systems included conventional tillage with rotation of rice and winter fallow system (CTF), conventional tillage with rotation of rice and rape system (CTR), no-till and ridge culture with rotation of rice and rape system (NT) and tillage and ridge culture with rotation of rice and rape system (TR). Soils were sampled in the spring of 2009 and sectioned into 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm depth, respectively.Tillage effect on SOC was observed, and SOC concentrations were much larger under NT than the other three tillage methods in all soil depths from 0 to 60 cm. The mean SOC concentration at 0–60 cm soil depth followed the sequence: NT (22.74 g kg^?1) > CTF (14.57 g kg^?1) > TR (13.10 g kg^?1) > CTR (11.92 g kg^?1). SOC concentrations under NT were significantly higher than TR and CTR (P < 0.01), and higher than CTF treatment (P < 0.05). The SOC storage was calculated on equivalent soil mass basis. Results showed that the highest SOC storage at 0–60 cm depth presented in NT, which was 158.52 Mg C ha^?1, followed by CTF (106.74 Mg C ha^?1), TR (93.11 Mg C ha^?1) and CTR (88.60 Mg C ha^?1). Compared with conventional tillage (CTF), the total SOC storage in NT increased by 48.51%, but decreased by 16.99% and 12.77% under CTR and TR treatments, respectively. The effect of tillage on DOC was significant at 0–10 cm soil layer, and DOC concentration was much higher under CTF than the other three treatments (P < 0.01). Throughout 0–60 cm soil depth, DOC concentrations were 32.92, 32.63, 26.79 and 22.10 mg kg^?1 under NT, CTF, CTR and TR, and the differences among the four treatments were not significant (P > 0.05). In conclusion, NT increased SOC concentration and storage compared to conventional tillage operation but not for DOC.     

Rainforest conversion to smallholder cash crops leads to varying declines of beetles (Coleoptera) on Sumatra

Southeast Asian arthropod biodiversity is in rapid decline, but the variability of responses within taxa has received little attention. Using canopy fogging, we collected ~50,000 beetles (Coleoptera) in (1) lowland rainforest, (2) jungle rubber (rubber agroforest), and smallholder monoculture plantations of (3) rubber and (4) oil palm in Sumatra, across two landscapes and seasons. On average, beetle abundance was more than 50%, and biomass over 75%, lower in rubber and oil palm plantations than in rainforest and jungle rubber. This pattern was influenced by landscape and season. Abundance and biomass declines were similar in Chrysomelidae, Elateridae, and Staphylinidae, but differed in Curculionidae, which were most abundant in oil palm due to the introduced oil palm pollinator Elaeidobius kamerunicus. Across beetle families, species richness in monocultures was reduced by at least 70% compared to rainforest, with beetle richness in jungle rubber being similar to rainforest. Community composition in oil palm plantations differed markedly from the other land-use systems for Chrysomelidae and Curculionidae, but less for Elateridae and Staphylinidae. Turnover contributed more to overall beta diversity than nestedness for all families and land-use systems. Likely undersampling of the beetle community in rainforest suggests that declines of beetle density and diversity are much more severe than reported here, especially for beetle families with many concealed species, such as Staphylinidae. This study provides first evidence that negative responses of beetles to tropical land-use change vary among families, and is the first report of its kind from heavily understudied Sumatra.     

Environmental Consequences of the Demise in Swidden Cultivation in Southeast Asia: Carbon Storage and Soil Quality

The effects of swidden cultivation on carbon storage and soil quality are outlined and compared to the effects of the intensified production systems that swidden systems of Southeast Asia transform into. Time-averaged aboveground carbon stocks decline by about 90% if the long fallow periods of traditional swidden cultivation are reduced to 4 years and by about 60% if swidden cultivation is converted to oil palm plantations. Stocks of soil organic carbon (SOC) in tree plantations are 0–40% lower than stocks in swidden cultivation, with the largest losses found in mechanically established oil palm plantations. Impacts of tree plantations on soil quality are to a large extent determined by management. Conversion of swiddening to continuous annual cropping systems brings about substantial losses of time-averaged aboveground carbon stocks, reductions of SOC stocks and generally leads to declining soil quality. Knowledge of carbon storage in belowground biomass of tree based systems of the tropics is sparse but failure to include this pool in carbon inventories may significantly underestimate the total biomass of the systems. Moreover, studies that consider the ecological reasons behind farmers’ land use decisions as well as spatial variability in biogeophysical and edaphological parameters are needed to evaluate the effects of the ongoing land use transitions in Southeast Asia.     

Influence of rhizospheric microbial inoculation and tolerant plant species on the rhizoremediation of lindane

Application of rhizospheric microbes to enhance the phytoremediation of organic pollutants has gained considerable attention recently due to their beneficial effects on the survival and growth of plants in contaminated soil sites. The present study was demonstrated to test the combined rhizoremediation potential of Staphylococcus cohnii subspecies urealyticus in the presence of tolerant plant Withania somnifera grown in lindane spiked soil. Withania was grown in garden soil spiked with 20 mg kg⁻¹ of lindane and inoculated with 100 ml of microbial culture (8.1 × 10⁶ CFU). Effect of microbial inoculation on plant growth, lindane uptake, microbial biomass carbon, dehydrogenase activity, residual lindane concentration and lindane dissipation percentage were analyzed. The microbial inoculation significantly enhances the growth and lindane uptake potential of test plant (p < 0.05). Furthermore, there was an enhanced dissipation of lindane observed in microbial inoculated soil than the dissipation rate in non-inoculated soil (p < 0.01) and the dissipation rate was positively correlated with the soil dehydrogenase activity and microbial biomass carbon (p < 0.05). The study concludes that the integrated use of tolerant plant species and rhizospheric microbial inoculation can enhance the dissipation of lindane, and have practical application for the in situ remediation of contaminated soils.     

Changes in soil microbial functional diversity under different vegetation restoration patterns for Hulunbeier Sandy Land

Grassland desertification seriously threatens economic and social sustainable development. How to control grassland desertification, and even to restore and reconstruct grassland has been paid much attention. Vegetation restoration is considered to be a very effective solution. Soil contains an immense diversity of microbes, and the characteristics of soil microbial communities are sensitive indicators of soil. It is important to understand the relationship between vegetation and soil microbial diversity during the restoration process. Based on Biolog-Eco technology, a case study was carried out to investigate the effects of five different vegetation restoration patterns on soil microbial functional diversity after four years in sandy land in Hulunbeier, China. The five vegetation restoration patterns included mono-cultivar planting of Agropyron cristatum (UA), mono-cultivar planting of Hedysarum fruticosum (UH), mono-cultivar planting of Caragana korshinskii (UC), and mixed-cultivar planting of A. cristatum and H. fruticosum (AC), mixed-cultivar planting of A. cristatum, H. fruticosum, C. korshinskii and Elymus nutans (ACHE). Completely degraded sandy land was used as control.The results indicated that the vegetation restoration significantly increased soil microbial activity. The Average Well Color Development (AWCD), which represents soil microbial metabolic activity, followed the order of UC > UH > UA > ACHE > AC > control. AWCD of five vegetation restoration patterns were all higher than that of control, and the highest soil microbial metabolic activity in mono-cultivar planting of C. korshinskii treatment was found. Five vegetation restoration patterns resulted in significant increase in Shannon index (H), evenness (E) and Simpson’s Dominance (D) of soil microbial community. Greater Shannon index and Simpson’s Dominance was observed in UC treatment than in other four vegetation restoration treatments and control. ACHE treatment had the highest evenness index (E) of soil microbial community. The principal component analysis (PCA) indicated a similar mode in carbon utilization for soil microbial community of UA, AC, ACHE and CK. However, UH and UC treatments had special carbon utilization mode. Treatments of UA, AC, ACHE and CK concentrated in the negative direction of the first principal component. Conversely, treatments of UH and UC concentrated in the positive direction of the first and second principal component respectively. The carbon sources mostly used by soil microbes were carbohydrates, amino acids, metabolic mediates and secondary metabolites. Therefore, vegetation restoration enhanced the metabolic activity and functional diversity of microbial community in sandy soil.     

Hemicellulose sugar recovery from steam-exploded wheat straw for microbial oil production

There are currently few successful examples of using straw hemicellulose as a carbon source in the fermentation industry. In this paper, hemicellulose hydrolysates were recovered from steam-exploded wheat straw (SEWS) and used to produce microbial oil. The effects of the steam explosion treatment conditions, the elution temperature and the ratio of elution water to SEWS on sugar recovery were examined. A broth with 3.8 g l^?1 of reducing sugar and 22.3 g l^?1 of total soluble sugars was obtained with a 10-fold excess (w/w) of water at 40 °C to wash the SEWS treated under steam explosion conditions at 200 °C for 5 min. This broth was used to produce microbial oil by the oleaginous fungus Microsphaeropsis sp., which was able to secrete xylanase to degrade oligosaccharides from straw hemicellulose and accumulate microbial oil. Under optimized conditions, the oil concentration was 2.6 g l^?1. The yield of oil from sugar consumed was 0.14 g g^?1. The microbial oil produced by this research could be used as feedstock for biodiesel production because the microbial oil was primarily composed of neutral lipids. This research establishes a novel protocol for microbial oil production from straw hemicellulose.     

Porous biocarrier-enhanced biodegradation of crude oil contaminated soil

Soil contamination with crude oil from petrochemicals and oil exploitation is an important worldwide issue. Comparing available remediation techniques, bioremediation is widely considered to be a cost-effective choice; however, slow degradation of crude oil is a common problem due to the low numbers of bacteria capable of degrading petroleum hydrocarbons and the low bioavailability of contaminants in soil. To promote crude oil removal, biocarrier for immobilization of indigenous hydrocarbon-degrading bacteria was developed using porous materials such as activated carbon and zeolite. Microbial biomass reached 10¹⁰ cells g^?1 on activated carbon and 10⁶ cells g^?1 on zeolite. Total microbial and dehydrogenase activities were approximately 12 times and 3 times higher, respectively, in activated carbon than in zeolite. High microbial colonization by spherical and rod shapes were observed for the 5–20 μm thick biofilm on the outer surface of both biocarriers using electronic microscopy. Based on batch-scale experiments containing free-living bacterial cultures and activated carbon biocarrier into crude oil contaminated soil, biocarrier enhanced the biodegradation of crude oil, with 48.89% removal, compared to natural attenuation with 13.0% removal, biostimulation (nutrient supplement only) with 26.3% removal, and bioaugmentation (free-living bacteria) with 37.4% removal. In addition, the biocarrier increased the bacterial population to 10⁸ cells g^?1 dry soil and total microbial activity to 3.5 A₄₉₀. A hypothesis model was proposed to explain the mechanism: the biocarrier improved the oxygen, nutrient mass transfer and water holding capacity of the soil, which were the limiting factors for biodegradation of non-aqueous phase liquid (NAPL) contaminants such as crude oil in soil.Scientific relevanceThis study explored the role of biocarrier in enhancing biodegradation of hydrophobic contaminants such as crude oil, and discussed the function of biocarrier in improving oxygen mass transfer and soil water holding capacity, etc.     

Changes in soil microbial community under willow coppice: The effect of irrigation with secondary-treated municipal wastewater

The effect of secondary-treated wastewater irrigation of a short-rotation willow coppice on soil microbial parameters was evaluated twice in 3 years using microbiological and biochemical properties. The soil metabolically active microbial biomass, basal respiration, N-mineralization, potential nitrification, alkaline and acid phosphatase and dehydrogenase activities were measured. The microbial community metabolic profile was determined with Biolog EcoPlates and bacterial community structure was assessed using denaturing gradient gel electrophoresis. After 2 years, a significant increase had occurred in soil microbial biomass, respiration and nitrogen mineralization activity both in the irrigated and in the non-treated plots. Wastewater irrigation increased the soil potassium concentration and enhanced the activity of alkaline phosphatase. Plant growth and irrigation affected the nitrogen mineralization activity—the increase was twice as high in the control plots as in the irrigated plots after 2 years. Potential nitrification, acid phosphatase activity and microbial community metabolic activity did not differ significantly (P > 0.05) between the control and the irrigated plots during the study. The comparison of soil profiles indicated that the observed increases in the soil microbiological parameters were allocated to the upper 10 cm. The establishment of willow plants on the fields affected the microbial community structure, with an increased diversity and higher similarity among the planted plots after 2 years. From our results we conclude that the willow coppice affected the soil bacterial community structure and had a positive effect on soil biological activity. Irrigation with pre-treated wastewater affected soil chemical and biochemical properties.     

A comparative assessment of support vector regression,artificial neural networks,and random forests for predicting and mapping soil organic carbon stocks across an Afromontane landscape

Soil organic carbon (SOC) is a key indicator of ecosystem health, with a great potential to affect climate change. This study aimed to develop, evaluate, and compare the performance of support vector regression (SVR), artificial neural network (ANN), and random forest (RF) models in predicting and mapping SOC stocks in the Eastern Mau Forest Reserve, Kenya. Auxiliary data, including soil sampling, climatic, topographic, and remotely-sensed data were used for model calibration. The calibrated models were applied to create prediction maps of SOC stocks that were validated using independent testing data. The results showed that the models overestimated SOC stocks. Random forest model with a mean error (ME) of −6.5 Mg C ha⁻¹ had the highest tendency for overestimation, while SVR model with an ME of −4.4 Mg C ha⁻¹ had the lowest tendency. Support vector regression model also had the lowest root mean squared error (RMSE) and the highest R² values (14.9 Mg C ha⁻¹ and 0.6, respectively); hence, it was the best method to predict SOC stocks. Artificial neural network predictions followed closely with RMSE, ME, and R² values of 15.5, −4.7, and 0.6, respectively. The three prediction maps broadly depicted similar spatial patterns of SOC stocks, with an increasing gradient of SOC stocks from east to west. The highest stocks were on the forest-dominated western and north-western parts, while the lowest stocks were on the cropland-dominated eastern part. The most important variable for explaining the observed spatial patterns of SOC stocks was total nitrogen concentration. Based on the close performance of SVR and ANN models, we proposed that both models should be calibrated, and then the best result applied for spatial prediction of target soil properties in other contexts.